Goodreads has a scanner in their app (on iOS/Android) that can scan covers although for some reason it automagically adds those books into a "to-read" shelf but I guess this isn't a problem for you if you create an account for the purpose.
The API is severely rate-limited (1rps), non-standard oath and badly documented, but you should be able to get some xml out of it and parse that however you'd like.